While not used in this experiment, two concepts important in human experiments are the placebo effect and blinding. The placebo effect is a psychological effect when a subject is told they are given a specific treatment and thus demonstrate effects of that treatment, despite being given an inert treatment. For example, if somebody was given non-alcoholic beer and told it was high in alcohol content, he would believe himself to be drunk.
Blinding is the practice of not telling the subjects and the observers which treatment has been applied. This is important because it negates a potential placebo effect. If the subject is unaware of his or her treatment, then they cannot be tricked that they would be affected one way. Double blinding is the practice of telling neither the subject nor the observer of the treatment used, so that there is no bias in demonstrating or observing results. For example, if a subject was given a pill and neither the subject nor the observer were told whether it was Advil or Xanax, then it would be an example of double blinding.